auto merge of #16942 : alexcrichton/rust/remove-net-assert, r=brson
auto merge of #16942 : alexcrichton/rust/remove-net-assert, r=brson

This assert was likely inherited from some point, but it's not quite valid as a
no-timeout read may enter this loop, but data could be stolen by any other read
after the socket is deemed readable.

I saw this fail in a recent bors run where the assertion was tripped.

mahkoh/rust,victorvde/rust,defuz/rust,KokaKiwi/rust,cllns/rust,pshc/rust,barosl/rust,ebfull/rust,XMPPwocky/rust,ruud-v-a/rust,gifnksm/rust,XMPPwocky/rust,cllns/rust,carols10cents/rust,mdinger/rust,zubron/rust,nwin/rust,zubron/rust,barosl/rust,krzysz00/rust,aidancully/rust,P1start/rust,sae-bom/rust,emk/rust,pelmers/rust,zubron/rust,seanrivera/rust,zaeleus/rust,TheNeikos/rust,omasanori/rust,philyoon/rust,bombless/rust,ruud-v-a/rust,rohitjoshi/rust,reem/rust,omasanori/rust,gifnksm/rust,ruud-v-a/rust,hauleth/rust,zubron/rust,andars/rust,robertg/rust,GBGamer/rust,jashank/rust,jashank/rust,gifnksm/rust,jroesch/rust,mahkoh/rust,pelmers/rust,l0kod/rust,0x73/rust,jroesch/rust,l0kod/rust,barosl/rust,zaeleus/rust,kimroen/rust,zubron/rust,defuz/rust,P1start/rust,bombless/rust,KokaKiwi/rust,carols10cents/rust,aidancully/rust,ebfull/rust,avdi/rust,robertg/rust,GBGamer/rust,robertg/rust,aepsil0n/rust,kimroen/rust,jashank/rust,seanrivera/rust,quornian/rust,avdi/rust,vhbit/rust,aneeshusa/rust,rprichard/rust,GBGamer/rust,ktossell/rust,kwantam/rust,jashank/rust,miniupnp/rust,avdi/rust,ejjeong/rust,sae-bom/rust,aneeshusa/rust,zachwick/rust,gifnksm/rust,ruud-v-a/rust,XMPPwocky/rust,zachwick/rust,mahkoh/rust,miniupnp/rust,dwillmer/rust,victorvde/rust,jroesch/rust,mihneadb/rust,dinfuehr/rust,krzysz00/rust,quornian/rust,dwillmer/rust,krzysz00/rust,nwin/rust,ebfull/rust,bombless/rust,defuz/rust,defuz/rust,P1start/rust,cllns/rust,0x73/rust,zachwick/rust,krzysz00/rust,pelmers/rust,richo/rust,mvdnes/rust,pelmers/rust,0x73/rust,emk/rust,barosl/rust,mihneadb/rust,XMPPwocky/rust,andars/rust,pshc/rust,bombless/rust,TheNeikos/rust,hauleth/rust,mdinger/rust,GBGamer/rust,dinfuehr/rust,dwillmer/rust,KokaKiwi/rust,vhbit/rust,miniupnp/rust,vhbit/rust,barosl/rust,ktossell/rust,mdinger/rust,vhbit/rust,ktossell/rust,untitaker/rust,zachwick/rust,kwantam/rust,ejjeong/rust,dinfuehr/rust,gifnksm/rust,ejjeong/rust,seanrivera/rust,P1start/rust,emk/rust,GBGamer/rust,mahkoh/rust,pshc/rust,0x73/rust,quornian/rust,0x73/rust,quornian/rust,ruud-v-a/rust,TheNeikos/rust,mahkoh/rust,dinfuehr/rust,jashank/rust,ruud-v-a/rust,mvdnes/rust,sae-bom/rust,omasanori/rust,mihneadb/rust,nwin/rust,AerialX/rust,GBGamer/rust,carols10cents/rust,ejjeong/rust,pelmers/rust,mvdnes/rust,reem/rust,omasanori/rust,richo/rust,pshc/rust,philyoon/rust,zaeleus/rust,KokaKiwi/rust,vhbit/rust,philyoon/rust,AerialX/rust-rt-minimal,jroesch/rust,aidancully/rust,reem/rust,sae-bom/rust,GBGamer/rust,seanrivera/rust,0x73/rust,XMPPwocky/rust,jashank/rust,dwillmer/rust,pshc/rust,bombless/rust-docs-chinese,ebfull/rust,hauleth/rust,graydon/rust,richo/rust,nwin/rust,AerialX/rust,bombless/rust,ebfull/rust,l0kod/rust,TheNeikos/rust,emk/rust,kimroen/rust,miniupnp/rust,AerialX/rust,mdinger/rust,l0kod/rust,ejjeong/rust,victorvde/rust,ktossell/rust,dwillmer/rust,rohitjoshi/rust,vhbit/rust,pshc/rust,untitaker/rust,kimroen/rust,XMPPwocky/rust,GBGamer/rust,hauleth/rust,reem/rust,cllns/rust,robertg/rust,aepsil0n/rust,graydon/rust,barosl/rust,ktossell/rust,kwantam/rust,0x73/rust,pshc/rust,miniupnp/rust,ejjeong/rust,KokaKiwi/rust,P1start/rust,miniupnp/rust,avdi/rust,robertg/rust,zubron/rust,dinfuehr/rust,dwillmer/rust,zaeleus/rust,mvdnes/rust,richo/rust,andars/rust,graydon/rust,rprichard/rust,kwantam/rust,miniupnp/rust,AerialX/rust-rt-minimal,kwantam/rust,seanrivera/rust,rohitjoshi/rust,krzysz00/rust,nwin/rust,avdi/rust,aepsil0n/rust,hauleth/rust,emk/rust,P1start/rust,carols10cents/rust,kimroen/rust,cllns/rust,gifnksm/rust,vhbit/rust,zachwick/rust,AerialX/rust,AerialX/rust,jroesch/rust,richo/rust,victorvde/rust,rprichard/rust,KokaKiwi/rust,avdi/rust,barosl/rust,zaeleus/rust,untitaker/rust,emk/rust,nwin/rust,sae-bom/rust,ktossell/rust,aneeshusa/rust,aneeshusa/rust,mihneadb/rust,reem/rust,bombless/rust,kimroen/rust,dwillmer/rust,graydon/rust,aidancully/rust,jashank/rust,mdinger/rust,robertg/rust,AerialX/rust,mihneadb/rust,seanrivera/rust,nwin/rust,andars/rust,kimroen/rust,omasanori/rust,aidancully/rust,jashank/rust,ebfull/rust,aepsil0n/rust,AerialX/rust-rt-minimal,quornian/rust,aneeshusa/rust,l0kod/rust,l0kod/rust,defuz/rust,quornian/rust,l0kod/rust,quornian/rust,miniupnp/rust,mahkoh/rust,AerialX/rust-rt-minimal,untitaker/rust,TheNeikos/rust,mvdnes/rust,carols10cents/rust,graydon/rust,sae-bom/rust,rohitjoshi/rust,andars/rust,rprichard/rust,richo/rust,AerialX/rust-rt-minimal,jroesch/rust,aepsil0n/rust,rprichard/rust,aepsil0n/rust,rohitjoshi/rust,AerialX/rust-rt-minimal,jroesch/rust,victorvde/rust,P1start/rust,dinfuehr/rust,carols10cents/rust,andars/rust,philyoon/rust,rohitjoshi/rust,krzysz00/rust,kwantam/rust,aneeshusa/rust,dwillmer/rust,zaeleus/rust,victorvde/rust,vhbit/rust,pshc/rust,pelmers/rust,zubron/rust,mihneadb/rust,reem/rust,omasanori/rust,emk/rust,zubron/rust,untitaker/rust,philyoon/rust,cllns/rust,ktossell/rust,l0kod/rust,mdinger/rust,philyoon/rust,aidancully/rust,graydon/rust,defuz/rust,TheNeikos/rust,zachwick/rust,jroesch/rust,mvdnes/rust,hauleth/rust,rprichard/rust,nwin/rust,untitaker/rust